The cornea performs functions critical for normal vision and maintenance of eye health, including providing about two-thirds of the optical power of the eye and protecting the eye from injury or infection. Corneal disease and injury is a leading cause of blindness worldwide. Many corneal disease and injuries can be treated by transplantation of donor corneas. The cornea is the most transplanted organ in the body and has a high success rate over 15 years. For example, approximately 40,000 corneal transplantations are performed per year in the U.S. However, demand for corneas for transplantation greatly exceeds the current supply worldwide, and the limited quality and quantity of available donor tissue hinders treatment. One factor contributing to the inadequate supply of donated corneas is that up to 30% of donated corneas are rejected for transplantation due to poor quality of the corneal endothelium. Quality of the corneal endothelium generally decreases with donor age because, as the cornea ages or is injured, the endothelial cells die and are not replaced. Therefore, as the population ages, the supply of donor tissue having suitably healthy corneal endothelium decreases. Moreover, the number and quality of donated corneas is expected to decline as the popularity of LASIK surgery increases (these corneas are rejected for transplantation).
Diseases of the cornea may involve one or more of the cornea's five layers: the corneal epithelium, Bowman's layer, the corneal stroma, Descemet's membrane, and the corneal endothelium. The corneal epithelium, corneal stroma, and corneal endothelium are cellular layers, while Bowman's layer and Descemet's membrane are primarily composed of collagen fibrils. The corneal endothelium is a single layer of cells on the inner surface of the cornea. It faces the chamber formed between the cornea and the iris and keeps the cornea transparent by regulating fluid levels. Without functional corneal endothelium, the cornea becomes cloudy and vision is lost. Properly functioning corneal endothelial cells maintain the proper fluid levels in the cornea, e.g., the balance between “leakage” of fluid into the stroma and active pumping that continuously operates to move fluid from the stroma to the anterior chamber of the eye.
Corneal endothelial cells have been reported to have little or no capacity to proliferate in vivo, such that they are not replaced when injured or otherwise lost. In humans, the corneal endothelial cell layer is most densely packed at birth and cell density thereafter decreases rapidly as the eyes grow (reflecting the same number of cells covering a larger area). Thereafter, corneal cell density gradually declines with age, apparently reflecting the gradual loss of cells which are not replaced. As cell density decreases, each cell spreads out and covers a larger area to maintain the cell layer's barrier and pump functions. However, once the cell density drops too low (lower than about 500 to 1000 cells/mm2) its function is compromised, resulting in corneal clouding, stromal edema, loss of visual acuity and eventual blindness. Specifically, the cell density of tightly packed corneal endothelium in vivo has been reported to be as high as 5624 cells/mm2 in infants two months of age, falling to 4252 cells/mm2 within the first year from birth, and subsequently decreasing rapidly during early childhood (associated with the increase in corneal size as eyes grow). By 5 years of age, corneal endothelium density falls to approximately 3591 plus or minus 399 cells/mm2, and falls farther to approximately 2697 plus or minus 246 cells/mm2 by 10 years of age, and further declines by approximately 0.6% per year throughout adulthood. See Peh et al., Transplantation. 2011 Apr. 27; 91(8):811-9.
Primary diseases that affect the corneal endothelium include Fuch's dystrophy, iridocorneal endothelial syndrome, posterior polymorphous dystrophy, and congenital hereditary endothelial dystrophy. Secondary diseases for which the most effective treatment is replacement of the corneal endothelium include several corneal dystrophies, contact lens usage, cataract surgery, and late endothelial failure in cornea transplantation. The preferred treatment when only the corneal endothelium is compromised is Descemet's stripping with endothelial keratoplasty (DSEK), which includes the removal of Descemet's membrane and the corneal endothelium, and subsequent transplantation of donor tissue. Alternatively, in penetrating keratoplasty (PKP) the entire cornea is removed and replaced.
Generally, corneal transplantation includes obtaining a donor cornea (e.g., from a post-mortem anatomical gift), determining whether the donor cornea is of sufficient quality and otherwise suitable for use, and surgical replacement of the damaged or diseased cornea. Procedures have been developed to replace the entire cornea (penetrating keratoplasty) or leave the patient's Descemet's membrane and endothelium and replace the remaining layers with donated tissue (lamellar keratoplasty); the latter procedure may decrease the risk of transplant rejection but may also give inferior visual acuity post-transplant. Additionally, lamellar keratoplasty may not be suitable for treatment of some conditions for which replacement of the patient's corneal endothelium and/or Descemet's membrane may be the indicated treatment. See, generally, U.S. Pat. No. 5,755,785, U.S. Pat. No. 5,649,944, U.S. Pat. No. 7,147,648, U.S. Pat. No. 7,300,653, U.S. Pat. No. 5,584,881, U.S. Pat. No. 5,686,414, U.S. Pat. No. 7,300,654, U.S. patent application Ser. No. 10/525,391, each of which is incorporated by reference in its entirety. Additional methods of corneal endothelial surgical replacement are under development, including Descemet's Membrane Endothelial Keratoplasty (DMEK), in which the donor tissue consists only of Descemet's membrane and corneal endothelium. Another potentially promising therapeutic avenue is corneal endothelial reconstruction, in which corneal endothelial cells are cultured in vitro prior to transplantation. For example, donated human corneal cells were cultured on a polymer, released onto a bioadhesive gelatin disc, and then successfully integrated into denuded rabbit corneas, with the gelatin disc dissolving after transplantation (Hsiue et al., Transplantation. 2006 Feb. 15; 81(3):473-6, which is incorporated by reference herein in its entirety). However, methods utilizing culture cells presuppose a source of said cells, and thus are affected by the shortage of suitable donated tissues as described above. Additionally, due to differences among donated cells, it may prove difficult to produce corneal endothelial cell cultures of consistent quality and efficacy. Regulatory hurdles may also make such methods logistically difficult to perform on a large scale, due to the possibility that extensive testing for safety and/or efficacy may be required for the cells obtained from each donor. These and additional therapeutic methods are further described in Thomas John, Corneal Endothelial Transplant: DSAEK, DMEK & DLEK (JP Medical Ltd, 2010), which is incorporated by reference herein in its entirety.
Additional disclosures generally related to methods of obtaining and using corneal cells, including therapeutic methods, culture methods, preservation methods, compositions containing or that that may be used in conjunction therewith, and the like are included in U.S. 2007/0275365, US 2010/0209402, US 2010/0233240, US 2011/0009488, US 2009/0232772, U.S. Pat. No. 5,166,048, US 2007/0092550, US 2005/0214259, US 2007/0148137, U.S. Pat. No. 4,959,319, U.S. Pat. No. 5,310,728, U.S. Pat. No. 5,589,451, US 2010/0215717, U.S. Pat. No. 5,703,047, US 2009/0222086, US 2009/0263465, US 2006/0228693, US 2006/0240552, US 2009/0270982, U.S. Pat. No. 5,269,812, U.S. Pat. No. 7,371,513, US 2010/0069915, and US 2011/0166650, each of which is incorporated by reference herein in its entirety.